Assuming you mean "SPL (dB, 1W/1m)", then there's no need: take the SPL figure and add or subtract as many decibels as compared to the 1W test figure. So if you put 10W through an 88dB/1W/1m rated speaker, you'll read 88 + 10*log(10W/1W) = 98dB. (In acoustical energy terms, this is 98 = 10*log(I/10^-12) ~= 6mW per square meter, in case you were wondering.)

How is this chart? It is from Richard Small. It has acoustic watts on the left, and the equivalent SPL on the right. It also tells you how much air must be moved in a sealed system to produce what SPL, (or acoustic watts) at which frequency.